This invention relates to a process for preparing perylene pigment compositions in the presence of certain non-pigmentary cyclic anhydrides or imides. Perylenes, including diimides of perylene-3,4,9,10-tetracarboxylic acid, can be prepared by methods known in the art. E.g., W. Herbst and K. Hunger, Industrial Organic Pigments, 2nd ed. (New York: VCH Publishers, Inc., 1997), pages 9 and 476-479; H. Zollinger, Color Chemistry (VCH Verlagsgessellschaft, 1991), pages 227-228 and 297-298; and M. A. Perkins, "Pyridines and Pyridones" in The Chemistry of Synthetic Dyes and Pigments, ed. H. A. Lubs (Malabar, Fla.: Robert E. Krieger Publishing Company, 1955), pages 481-482; see also U.S. Pat. Nos. 4,431,806, 4,496,731, 4,797,162, 5,248,774, 5,264,034, and 5,466,807. Perylenes as initially isolated in the process of the present invention, often referred to as crude perylenes, are generally unsuitable for use as pigments and thus must be subjected to one or more additional finishing steps that modify particle size, particle shape, and/or crystal structure in such a way that provides good pigmentary quality. See, for example, K. Merkle and H. Schafer, "Surface Treatment of Organic Pigments" in Pigment Handbook, Vol. III (New York: John Wiley & Sons, Inc., 1973), page 157; R. B. McKay, "The Development of Organic Pigments with Particular Reference to Physical Form and Consequent Behavior in Use" in Rev. Prog. Coloration, 10, 25-32 (1979); and R. B. McKay, "Control of the application performance of classical organic pigments" in JOCCA, 89-93 (1989).
The addition of certain perylene derivatives to the ring-closure step has also been reported. For example, U.S. Pat. No. 5,264,034 discloses the use of certain perylene bis-imides or imide-anhydrides to improve the coloristic and rheological properties of perylene pigments. U.S. Pat. No. 5,248,774 discloses certain zwitterionic perylene bis-imide derivatives for use as colorants or as surface-modifying agents for known perylene pigments. U.S. Pat. No. 5,472,494 discloses the use of certain perylene mono-imide derivatives to modify the properties of organic pigments. These patents do not, however, disclose the non-pigmentary cyclic anhydrides and imides of the present invention.
It has now been found that the presence of certain non-pigmentary cyclic anhydrides and imides during the chemical synthesis of perylene bis-imides provides perylene pigment compositions that have improved transparency and color properties, even in the unfinished form that is initially isolated, and that are especially suitable for use in metallic paints.
Non-pigmentary cyclic anhydrides and imides of the type used in the present invention are known. E.g., U.S. Pat. No. 4,992,204 and J. M. Chapman, Jr. et al, J. Pharm. Sci., 78, 903-909 (1989). Such compounds have not, however, been used in combination with organic pigments.
Non-pigmentary naphthalimide derivatives have been disclosed in a journal article describing computer design of additives for improving the pigment properties of Pigment Red 179, an N,N-disubstituted perylene pigment. P. Erk et al, Eur. Coat. J., 10, 906-910 (1997). The article describes the naphthalimides as being poor growth inhibitors compared to perylene derivatives and does not disclose their incorporation during pigment synthesis. Furthermore, non-pigmentary cyclic anhydrides and imides of the type used in the present invention are not disclosed.